The present invention relates to first a method for operating an internal combustion engine, in which a real quantity of fuel, which is lead from a high-pressure region of a fuel system into a combustion chamber of the internal combustion engine, is dependent on a rated rotational moment. The control duration of a volume control valve, with which the volume of fuel that is supplied into the high-pressure region from a fuel pump can be affected, depends on the difference between a desired pressure and an intermediate pressure in the high-pressure region, and in which the supply output of the fuel pump, which is supplied into the high-pressure region, depend on the rotational speed of a drive shaft of the fuel pump.
This type of method is known from the market. A combustion engine with a fuel system is known, which includes an electric fuel pump that supplies the fuel from a fuel container to a high-pressure fuel pump. From this, the fuel is lead into a fuel collection line (xe2x80x9crailxe2x80x9d), in which the fuel is stored under high pressure. Injectors are connected to the fuel collection line, which inject the fuel directly into the combustion chamber of the engine. Through the volume control valve, the pressure side of the high-pressure fuel pump can be short circuited during a supply stroke with the suction side. This enables the introduction of the fuel quantity supplied to the fuel controlling line.
The amount of the fuel fed into the combustion chamber results from the injection duration of the injectors. This depends on one hand on the real rotational moment of the internal combustion engine and on the other hand, on the pressure which exists in the high-pressure region to which the injectors are connected. For a determined real rotational moment, the injectors are open longer with a lower pressure in the high-pressure region than with a higher pressure. The pressure in the high-pressure region is detected by a pressure sensor. The injection time of the injectors is increased with a fuel pressure that is determined to be too small due to an error in the sensor, which can lead to an undesired acceleration of the vehicle. On this basis, the function of the pressure sensor is monitored.
However, it is not completely out of the question that in determined situations that an unwanted acceleration of the vehicle can occur, in which such an internal combustion engine is included. It is therefore one object of the present invention to provide an improved method of the above-described type so that the internal combustion engine always works controllably.
This problem is resolved with a method, which from a desired control duration of the volume control valve, the determined rotational speed of the drive shaft of the fuel pump or the determined rotational speed of a crank shaft of the combustion engine driven by the fuel pump and the determined pressure in the high-pressure region, a test-fuel quantity is determined and is compared with the real fuel quantity determined from the real rotational moment.
With the method of the present invention, it is possible to not only monitor the functioning of the pressure sensor, rather to monitor entirely the determination of the fuel quantity to be injected. In this manner, such situations can be identified in which the pressure sensor works error-free, however, other values are incorrect, from which the fuel quantity actually to be injected from the injectors depends. This can be the situation, for example, when the real fuel quantity from the real rotational moment is accepted in error. An incorrect acceptance of the control duration of the volume control valve is also possible, however.
With the method of the present invention, also such errors can be known doubtfree. This occurs thereby that the fuel quantity, which should be injected into the combustion chamber of the engine, is recalculated over the real control duration of the volume control valve, over, for example, the rotational speed of the crank shaft of the internal combustion engine determined from a sensor, and over the pressure in the high-pressure region determined by a sensor.
Underlying this concept is that each fuel volume that is called from the injectors from the fuel controlling line must be again subsequently supplied from the second fuel pump in order to correctly maintain a determined pressure in the fuel controlling line. The supply volume of the second fuel pump depends in turn on the control time, or the closing duration, of the volume control valve and the rotational speed of the drive shaft of the second fuel pump. Since this is usually driven by the camshaft of the internal combustion engine, here the rotational speed of the engine, which typically is determined from on its crankshaft, can be used.
The inventive method, therefore, can be performed without requiring additional components. In the most cost-efficient manner, the operation of the internal combustion engine can be made more reliably and dependably.
In a first further development, it is proposed that the difference from the test fuel quantity and the real fuel quantity is created and the total difference is compared with a threshold value. Thereby, in a simple manner, a tolerance graph is produced, through which a dependable branching-off between the test fuel quantity and the real fuel quantity is defined. Through such a tolerance graph, for example, a dynamic effects, additional measurement accuracy, and so forth can be considered.
Therefore, it is possible that the test fuel quantity is determined by means of two characteristic curves. These characteristic curves are only dependent on the rotational speed of the fuel pump, or the internal combustion engine, and the fuel pressure in the high-pressure region. This is very simple to realize.
Alternatively, it is also possible that the test fuel quantity is determined by means of a multi-dimensional performance graph. The expense here is indeed larger, however, the accuracy and speed of calculation are better.
Particularly preferable is each further development of the inventive method, in which the performance of the comparison between the test fuel quantity and the real fuel quantity depends on the rotational speed of the crankshaft of the internal combustion engine. In this manner, the actual calculation shows that the test fuel quantity depending on the rotational speed quite differently affects normal and system-related tolerances of individual components.
It is especially preferable that with low rotational speeds of the internal combustion engine, in particular, below approximately 122 rpm, no comparison between test fuel quantity and real fuel quantity takes place. In particular, with such low rotational speeds, a comparison between test fuel quantity and real fuel quantity makes little sense, since the normal tolerances of the individual components of the engine in this rotational speed region already can lead to marked departures of the test fuel quantity from the real fuel quantity.
It is also advantageous in each embodiment of the method of the present invention that an error message or signal occurs and/or an alarm is released when the test fuel quantity and the real fuel quantity diverge more than is permitted from one another. The error message, for example, can be read out upon maintenance, so that the maintenance provider receives direction information and the necessary repairs can be made. In this manner, the maintenance of the engine is made easier. An alarm signals to the user of the engine directly that the engine is no longer functioning error-free. In the case of the use of the engine in a motor vehicle, the alarm signal can be included as a warning light on the dashboard, for example.
In a further embodiment, it is proposed that, based on an error message, a safety step is performed. When the comparison of the test fuel quantity with the real fuel quantity provides that the danger exists that the fuel quantity is or would be determined in error, and therewith the actual, produced rotational moment does not correspond to the desired rotational moment of the user of the engine, through the introduction of such a safety step, the operation of the engine that can pose a danger for the components of the engine and the life of the user can be prevented.
In order to prevent that such a safety measure is produced unnecessarily, it is proposed that the safety measure is only performed when the error message is produced over a determined amount of time. With this embodiment of the inventive method, short and one-time measurement error and/or calculator errors do not lead to an initiation of a safety step. This is limited to each case in which a continual, serious error is determined based on the comparison between the testing fuel quantity and the real fuel quantity.
Further, it is proposed that the safety mechanism includes an actuator of the fuel supply. This means only that the internal combustion engine is switched off. Through this radical safety step, further incorrect operation of the internal combustion engine leading to further damage is prevented. Also, a risk for the user of such an incorrectly operating engine is thereby reduced.
The invention relates also to a computer program, which is suited for performing the above-described method, when it is performed on a computer. Thereby, it is especially preferable when the computer program is stored on a storage, in particular, on a flash memory.
Further, the invention relates to a control and/or regulating apparatus for operating an internal combustion engine. In order to improve the safety upon operation of such an engine, it is proposed that the control and/or regulating apparatus includes a storage, on which a computer program of the above-describe type if stored.